Heart disease is caused by a build-up of cholesterol fats and/or atherosclerotic plaque and/or atherosclerotic lesions within coronary arteries. Over time these lesions grow, progressively narrowing the arteries, thereby restricting the quantity of blood flowing through the artery. Atherosclerosis can lead to myocardial infarction, angina pectoris and/or possibly also be a contributing factor inducing strokes. Heart disease is one of the leading causes of death throughout the world. Those who survive the consequences of heart disease generally experience prolonged suffering and possibly also disability.
Percutaneous transluminal coronary angioplasty (PTCA) is a technique used to clear occluded coronary arteries. Generally a stent is permanently placed within a vessel to hold the lumen open after PTCA, thus reinforcing the vessel wall and improving blood flow. Typically, a stent is a cylindrical shaped device formed from metal or polymers. One form of stent is radially compressed to a diameter that is smaller than that of the vessel in which it is to be deployed to enable it to be delivered to the treatment site. Once the stent has been delivered to the treatment site, it is expanded radially to allow it to contact and support the vessel wall. This type of stent can be crimped onto an expansion device such as a balloon catheter for delivery. Other stent types are fabricated elastically to resist compression in a free state and are releasably compressed for delivery. Both types of stent are expanded radially at the treatment site. Problems can arise if the stent does not fully expand, as the position of the stent may promote the formation of undesirable thrombi. Balloon angioplasty is a procedure in which PTCA is performed and a stent is deployed at the treatment site using a balloon catheter.
Typically, introduction of a stent that elastically resists compression involves introduction of a guidewire percutaneously. The guidewire is then steered to the treatment site through the vascular system. The stent is provided on the distal end of a catheter, which is advanced over the guidewire to the treatment site. The stent is deployed at this site, providing support to a damaged and/or collapsed vessel wall. The radially expandable stent is introduced in a similar manner, however the stent is crimped onto a balloon positioned at the distal end of the catheter and deployment of the stent at the treatment site is effected by inflation of the balloon. A similarly introduced stent could also be used to repair a dissection of a vessel or an aneurysm. Other problems may arise, if gradually over time the stent moves from its original position at the treatment site leaving a weak and vulnerable area of the vessel exposed.
Worldwide figures estimate that approximately 110 million people suffer from diabetes. Recent projections suggest that this figure will have doubled in 10 years. One of the consequences of diabetes is that the blood vessel walls are thinner, consequently the vessels are weaker. Studies have indicated that diabetic patients are more likely to suffer follow-on post balloon angioplasty complications with a five-year mortality rate of approximately 35%. Conversely diabetic patients who have undergone bypass surgery have a five-year mortality rate of 19%. However bypass surgery typically involves considerable trauma, pain and long periods of convalescence.
It is desirable to combine the advantage of coronary artery bypass surgery with the minimally invasive angioplasty/stent delivery technique.
Typically coronary artery bypass graft surgery requires open-chest surgery, which involves an eight to ten-inch incision made in the chest, a thoracotomy. A variety of minimally invasive cardiac surgical techniques have been developed such as the da Vinci technique, which involves robotically assisted surgery requiring only three pencil-sized holes made between the ribs. Through these holes, two robotic-arms and an endoscope (a tiny camera) gain access to the heart, making surgery possible without opening the chest. Coronary artery bypass graft surgery (CABG) is the most commonly performed “open heart” operation. There are approximately 375,000 CABG surgeries performed in the United States each year. Studies show that patients who have minimally invasive operations are released from hospital one to two days earlier than patients recovering from conventional cardiac surgery. Other advantages of minimally invasive surgery can include quicker patient recovery times, less pain, and significantly less scarring than traditional open-heart operations.
However, adoption of new techniques such as the da Vinci technique is typically slow as the specific skill requirements are difficult to acquire and the techniques are more difficult to perform than the traditional by-pass surgery. Many of the new techniques involve direct vascularisation from the ventricle of the heart.
Numerous devices and delivery systems that facilitate these new techniques are disclosed in the prior art.
U.S. Pat. No. 6,113,630 discloses an L-shaped transmyocardial implant, one leg of the L-shaped implant inserts into the coronary artery whilst the other leg inserts into the left ventricle of the heart through the myocardium. The portion of the implant that is positioned in the myocardium has a fabric cuff encircling the exterior surface that is used to integrate the implant with the myocardium and help prevent migration of the implant.
WO 00/15148 discloses a transmyocardial stent that provides a bypass around an occlusion in a coronary artery. The conduit has a section of a blood vessel attached to its interior lumen. Preferably, the section of blood vessel includes at least one naturally occurring one-way valve to prevent the backflow of blood from the coronary artery into the heart chamber.
WO 01/10348 discloses a method and apparatus relating to a conduit placed in the heart wall between the left ventricle and the coronary artery.
WO 00/21461 discloses devices and methods for delivering conduits into the wall of a patient's heart to communicate a coronary vessel with a heart chamber. The device includes a conduit support member which may be in the form of a shaft having a step which defines a recessed portion that receives the conduit. The conduit is covered by a sheath to protect tissue and/or the conduit during its delivery into the heart wall. The sheath is preferably tapered to aid in dilating the opening in the heart wall. The device preferably includes a dilator having a sharpened end and an enlarged end configured to be grasped to manipulate the dilator. There is also an actuator for allowing the sheath to be selectively moved to expose the conduit. The actuator includes a spring for biasing the sheath in a proximal direction.